426
ANALYTICAL CHEMISTRY
Certain groups are necessary for the formation of these important analytical substances. Among these are -OH, -COzH, =NOH, -CO--, and -NH2. T h e 5- and 6-membered rings found in chelate compounds are possible only when t h e acidic and/or coordinating groups necessary for their formation are properly located in t h e molecule with respect t o one another. With these principles clearly understood, t h e search for new reagents is greatly simplified. Interference is a major problem of t h e analytical chemist. One of t h e desirable objectives in t h e application of organic compounds in chemical analysis is the development of specific or highly selective procedures. Certain atomic groupings confer t h e property of specificity or selectivity on organic molecules. For example, t h e a-dioximes yield red precipitates with nickel salts, and the a-acyloin oximes form insoluble green copper salts. Finally, both sensitivity and selectivity m a y be improved by a n understanding of weight and volume effects, steric consideration, and by a knowledge of t h e solubilizing influence of certain atomic groupings. Coulometric Titrations. W. D. COOKE,Cornel1 University, Ithaca,
Ir;. Y.
-4 discussion of t h e historical aspects of coulometric analysis, principles of electrolytic oxidation and reduction, various types of procedures, and the advantages and disadvantages a s compared t o conventional procedures, instrumentation, and problems in continuous analysis. High precision coulometric titrations, the present status and some problems in analyses a t extreme dilution, a n electrometric approach to millimicrogram and micromicrogram samples, and some new endpoint techniques and their applications. Quantitative Organic Analysis Via Functional Groups. SIGGIA,General Aniline and Film Co., Easton, Pa.
SIDNEY
Applicability of this type of analysis t o t h e needs of t h e organic analyst. Fundamental principles involved in choosing reactions to be used for the analyses and how these principles are applied. Problems t h a t can arise when using a certain reaction and how these problems are overcome or circumvented. Reaction completeness, equilibrium, solvent and titration problems (discussion of nonaqueous titrations). Interferences. iivoiding separation of components. Separating components (distillation, extraction, precipitation, dialysis, electrodialysis, chromatographic adsorption, electrophoresis). Identification techniques using quantitative functional group analysis. Radioactivity Analysis. S. A. REYNOLDS, Oak Ridge National Laboratory, Oak Ridge, Tenn. DEFINITIOX A N D SCOPE. Determination of the quantity of radioactivity present, also, in many cases, the nuclide(s) responsible for t h e activity (qualitatively or quantitatively), IXSTRUMESTAL METHODS OF ANALYSIS. Measurement of radioactivity. Alpha: proportional counter. Beta: Geiger-Mtiller, proportional, and 1007&geometry counters. Gamma: G-M and proportional counters, ionization chambers, and scintillation counters. Decay Studies. Resolution of decay curves. Special instruments. Energy Measurements. Absorption techniques. Beta-ray spectrometry. Scintillation spectrometry. Alpha measurements. X-ray measurements, TECHNIQUES. Separations without “carrier.” SolSEPARATION vent extraction, distillation, electrodeposition, ion exchange. Separations with added carrier. Isotopic and nonisotopic carriers. Qualitative analysis: scheme, nucleonic aids. Quantitative analysis: yield correction, advantages, difficulties (scattering, etc.). APPLICATIONS.Radioisotope assay. Methods for common radioisotopes. Accuracy. Fission-product methods. Philosophy. Examples. Tracers in analytical chemistry. Application of above principles in use of radioactive tracers in conventional analytical chemistry. Separation and Analysis of Sugars and Related Compounds by Ion Exchange Chromatography. L. P. ZILL,Oak Ridge National Laboratory, Oak Ridge, Tenn. Analytical usefulness of a method for the separation and analysis of sugars and related compounds.
Previous observations on t h e formation of ionic complexes of sugars by reaction with borate ions. Application of ion exchange chromatography to the separation of borate-sugar complexes. Quantitative analysis of t h e separated sugars. Analysis of synthetic and natural sugar mixtures. Extension of the method to other polyhydroxy compounds such as t h e sugar alcohols, glycosides, nucleotides, etc. Future studies and applications of the method. Micromethods for Characterization of Organic Compounds. D. CHERONIS, Brooklyn College, Brooklyn, N. Y. NICHOLAS T h e classical approach in dealing with an unknown organic compound involves: (1) purification and determination of t h e purity of the unknown; (2) systematic study to ascertain whether t h e compound in question does or does not bear complete similarity in physical and chemical properties t o one of t h e large number of organic substances described in t h e chemical literature; (3) determination of t h e structure and classification if the compound under study is not known. Micromethods were discussed in detail: T h e concepts of “absolute” and “operational” purity. Criteria used in t h e establishment of purity: solubility, melting point, boiling point, optical properties, distribution between immiscible solvents. Problems involved in proof of identity. Rigorous proof based upon similarity of physical and chemical properties and upon similarity of one or two properties. T h e traditional approach for establishing whether a n unknown solid consists substantially of one component or two or more is simplified by the introduction of optical methods. Among t h e simpler ones is t h e microscopical examination of melting and crystallization phenomena, by which it is possible t o determine rapidly: crystal habit, formation of eutectic, melting temperature, and refractive index of t h e melt. Micromethods for the preliminary examination of liquids. Determination of melting points. -4critical discussion of all methods used for t h e determination of capillary and micro melting points. T h e need for better methods of frequent restandardiaation of thermometers. T h e confusion of the “melting points of organic compounds.” T h e effect of strains in t h e crystal lattice. Steps used in various schemes of systematic characterization. Classification of the unknown based upon: solubility and elements present; ionization constants and elements present. Further restriction of classification of unknown by means of “functional group tests.” Selection of tests and problems involved in application and limitation of the tests. Brief discussion of some new tests: chromatographic (paper) and use of tetrazolium salts for detection of reducing groups. Coordination of data and deduption of probable identity. Final proof of identity by derivization. Discussion of factors involved in t h e selection of derivatives. Critical discussion of effect of t h e purity of deriritiaing agent; ratio of reactants; effect of preparative and purification procedures; problems involved in coordinating observable melting point data with values listed in t h e literature. Simplification of the systematic approach by t h e experienced worker. Illustration of short cuts in t h e identification of organic compounds in very small amounts of samples: analysis of 2 drops of liquid used for doping of race horses; identification of t h e active component in a beauty finger nail preparation; identification of t h e active components in a remedy used for athlete’s foot.
In t h e book “Reagent Chemicals, American Chemical Society Specifications, 1950” o n p a g e 41 u n d e r t h e heading “Substances darkened b y h o t sulfuric acid” t h e t h i r d line was repeated a s the fifth line. T h e fifth line should r e a d : “(in a brine b a t h ) for 30 minutes, keeping t h e t e s t t u b e covered with a , ”
